7 
65 
Some striking contrasts and resemblances are shown in a comparison 
of these plots. Of the 21 species found in Plot A (see Pl. XXXIV) and 
the 15 found in Plot H (see Pl. 1), only 3 are common to both; one 
of these, Polyosma philippinensis, is represented by 3 individuals; the 
second, Myrica rubra, by 10 individuals, and the third, Quercus, by 14 
in A and 2 in H; however, this latter may represent two species. To 
what then is this difference in vegetation due? It can not alone, if at 
all, be ascribed to a lower temperature, for this factor is but a small one. 
The depth and character of the soil are approximately the same, for 
both plots have shallow soil composed principally of half-disintegrated 
voleanic rock. Precipitous slopes on each of the sides of the ridges 
characterize both situations. The difference can not then be due to the 
water-holding capacity of the soil, for if anything, as will be shown 
presently, the soil in the higher situation has more water than that in 
the lower, yet the tree vegetation in the former is more xerophytie than 
in the latter—that is, the trees are more stunted and the leaves are harder, 
smaller, and more leathery. This point is clearly demonstrated in the 
species common to both situations: the oaks invariably have smaller and 
harder leaves; a specimen of Calophyllum whitfordii, collected from a 
stunted tree near Plot A, at first gave rise to the belief that this was a 
species distinct from that found at lower and more protected altitudes 
in the Shorea-Plectronia formation, but when fertile specimens were 
collected in Plot TH from a still more stunted tree and with still more 
reduced and hardened leaves, the series was complete, extending from 
the comparatively mesophytic leaves taken from tall trees in the Shorea- 
Plectronia formation, through the less mesophytic forms found near 
Plot A, to the xerophytic leaves of that found on H. (See Pls. XLITI. 
XLIV, XLV.) The same may be said of other species, such as Myrica 
rubra, common to the three situations. (See Pl. XLIV.) These grada- 
tions can be extended so as to include many species not common to the 
two plots under consideration, but found in different ecological condi- 
tions from the base to the summit of the mountain and which systematists 
are tempted to, and often do, separate as distinct species, if ecological 
gradations between the two extremes are not in their possession. (See 
Pls. XLITT, XLIV, XLV.) These cases only illustrate the fact which 
has been so often emphasized for plants occurring in the temperate zone, 
that species capable of sufficient plasticity can adapt themselves to condi- 
tions in sucha manner as to grow in various ecological situations. But 
few have this power of wide life-range, and so it happens that different 
ecological aspects show different species, rather than -different forms of 
the same one. This latter fact is strikingly illustrated by the largest 
number of individuals on the ridge under consideration. (See Pl. XLV.) 
Hugenia congesta found in the upper five plots has orbicular, very leathery 
leaves, while Hugenia acuminatissima, in the lower four plots, has small, 
43814 —6 
